Structural, Electrical and Raman Characterization of AgNP-coated Porous Silicon SERS Substrate for Detection of Dengue NS1 Protein

Abstract

Surface Enhanced Raman Spectroscopy (SERS) is a specific and sensitive analytic technique suitable for detection of low concentration analyte. However, the performance of SERS is highly dependent on the type of SERS substrate used. In this study, solid base SERS substrates are fabricated for detection of low concentration dengue non-structural protein 1 (NS1) in saliva. Using an n-type phosphorous dopant, microstructural porous silicon (PSi) was fabricated using direct current electrochemical method. The PSi was deposited with different sizes of silver nanoparticles (AgNP) to increase the strength of electromagnetic field on the PSi surface. Here, the structural, electrical and Raman characterization of the fabricated AgNP coated PSi are presented. FESEM images show the cross-shaped surface structure of the substrate. The I-V curve reveals that the 75nm-AgNP samples produce better electrical conductivity property than the others. It is also observed that etching longer than a threshold reduces the conductivity performance of the substrate substantially, due to increase in the surface porosity. From Raman spectrum, the silicon peak at 520cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> shows a decreasing trend in intensity for samples with 30 min of etching. Interestingly, this observation complements that reported in our previous paper, where etching time of more than 28 min is found not suitable for producing uniform structure of PSi. The consistency between the structural, conductivity and Raman intensity can be used as indicators in developing good SERS substrate for non-invasive detection of low concentration dengue NS1 protein in saliva.